1. Field of the Invention
This invention relates in general to concrete and steel composite structures, such as used in bridge construction and repair, and more particularly, to the use of modular composite structural members used in new construction and in the repair of old structures utilizing existing girders. The invention further relates to apparatus and methods for connecting longitudinal and transverse joints in such structures and making shear connections at such joints.
2. Description of the Prior Art
Large structures, such as bridges are well known and are obviously time-consuming to build or widen and even more time-consuming to rehabilitate. Typically, a bridge structure will have longitudinally extending girders with a concrete deck surface. The concrete deck surface is usually made composite with the girders by pouring the concrete in place around shear connectors connected to the girders.
To originally form such composite members of the type having an upper concrete surface and a metal or concrete support underneath, a mold typically is utilized. First, the steel or concrete supports, such as girders or beams, are placed beneath the mold assembly disposed around and supported by the supports. Next, concrete is poured into the mold such that the concrete fills the mold and extends over the girders or beams. When the concrete has hardened, the mold pieces are disassembled from around the support such that the concrete rests on the supports. In such instances, these types of structural members are formed in place. This is usually advantageous so the concrete deck surface can better fit into the finished structure. The concrete deck portion is attached to the girders by shear connectors which are molded into the concrete. This technique works satisfactorily in many cases, particularly in original bridge construction where the area of construction is readily accessible and speed of construction is not a concern.
In previous systems where separate prefabricated units are used, the sections are positioned adjacent to one another upon support members for those sections, such as girders or beams, which have been positioned on the piers or abutments. This technique is particularly useful when it is not feasible to form the entire structure in place or when the use of prefabricated members can save construction time on site. It also works well in bridge widening projects where prefabricated members are installed next to the existing structure.
Certain construction restraints, such as those in which a bridge structure is being repaired or otherwise refurbished or rehabilitated, make many prior art methods of construction more expensive and result in associated problems, such as traffic delays. In repair or refurbishing, typically the old concrete deck, or at least a part of it, is removed, and another deck must be put in its place. If the replacement deck must be poured in place, molds must be set up, the concrete poured, and then the concrete allowed time to cure before the bridge structure can be reopened to traffic. In high density traffic areas, this creates considerable traffic tie-up problems, which result in significant lost time and inconvenience to commuters and other travelers.
The use of prefabricated composite units which can be set in place, such as those described above, greatly reduces the repair time involved. That is, the old structure may be removed, and the new structure simply set in place on the piers or abutments and attached to them. Because of the prefabrication, the time necessary to construct molds, pour concrete and allow the concrete to cure can all occur prior to the placement of the composite units. Thus, the “down time” to repair the bridge structure is greatly reduced, which lowers costs and pleases motorists. However, this technique creates longitudinal and transverse joints that need to be properly made so that the upper road surface is smooth and without misaligned upper surfaces. Also, it is important that the longitudinal and transverse joints be filled so that they do not become potential pathways for water and salt-laden water to fall objectionably on other parts of the structure.
The present invention all but eliminates this objectionable leakage without adding construction time to a constrained time window, such as occurs in overnight construction. Because the modular units or modules can be attached quickly, they can carry traffic very soon after they are placed in position. In the present invention, prefabricated composite modules are still positioned adjacent to one another, forming longitudinal and transverse joints therebetween. One of the adjacent modules is pulled and clamped to the other by a precompression technique which holds the adjacent modules together. A shear connection is made between the adjacent units and with the corresponding existing girder over which the longitudinal joint between the modules extends. Leveling bolts are utilized to level adjacent concrete deck portions of the modules so that upper surfaces thereof are level prior to final connections.
The joints may be filled with a sealant applied to the abutting faces of the joints before they are pulled together. Whether used with match-cast, abutting faces or a conventional, hardened, grout-filled joint, precompressing the joint has the advantage of creating an extremely water-tight joint and, at the same time, supplementing the tensile resistance of the joint adhesive with precompressive stresses.
One conventional approach to precompressing bridge structures is to install conduit in the deck portions thereof which is accomplished by positioning the conduit and pouring the moldable material around it. Steel cables are installed in these conduits after the bridge structure is erected and compression applied to the structures in a transverse direction by post-tensioning the steel cables. This process has several problems, one of which is the difficulty of aligning the conduits during the erection of the bridge structure. Further, there is a potential for damaging both the cable and its protective coating when the cable is pulled through misaligned conduit. Additionally, any such damage may result in future deterioration which is not visible and can lead to unexpected and sudden failure. In the present invention, any future deterioration of the precompressive components is readily visible and more easily corrected than with hidden and buried cable. Further, the present invention provides easy disassembly of the structure when future repair and/or rehabilitation is required, thus even further speeding up the rehabilitation time. Finally, due to the cost and extensive time of installation, splices of conventional post-tensioning are usually avoided. Thus, full roadway width installation is required, whereas the present invention allows as little as beam-to-adjacent-beam installation. The latter provides a substantial advantage over full-width installation in that only a portion of the traffic capacity is disabled instead of all of it.